Add support for reading configuration from a file

[omerlh]

Is your feature request related to a problem? Please describe.
Storing sensitive configuration in an environment variables is not considered as best practices.

Describe the solution you'd like
Allow reading configuration from a file or from a cli argument (look like it's supported by the config lib that in use).

[Jusshersmith]

Hi @omerlh! 👋

Thanks for sending this through. As you mentioned, the configuration library that we're now making use of (as of v2.0.0) should help with this! I believe we're still looking to utilise that library on the proxy side (right now, it's only being used by the auth side I believe), but once that's done I think this should be much more achievable.

I hope that is something that we can implement in the not too distant future. Though I wouldn't necessarily expect the abstraction of being able to store these variables in a file would be included in that change set; I don't think it's something we (BuzzFeed) would be able to prioritise, but I'll aim to post back here once we've finished the initial change set to clarify.